In recent years, various flat panel displays have been developed. Particularly, organic Electro Luminescence (EL) display devices including organic EL display elements are receiving great attention as excellent displays because a low power consumption, reduced thickness, higher picture quality, and the like can be achieved.
Further, display devices without a need for including a backlight, such as organic EL display devices and display devices including reflective liquid crystal display elements, are in a high demand to be flexible display devices so as to be freely bendable.
To achieve a flexible display device, there is a method for using a flexible substrate (flexible substrate) made of, for example, polyimide (PI) and the like and forming a thin film transistor element (TFT element) and a display element directly on the flexible substrate by a manufacturing step at a temperature less than or equal to a temperature that this flexible substrate can endure.
However, for this method, the temperature of the step of forming a TFT element and a display element needs to be less than or equal to the temperature at which a flexible substrate made of polyimide (PI) and the like can endure. Thus, a TFT element and a display element that can satisfy both aspects of element performance and reliability cannot be obtained. Accordingly, a method for manufacturing a flexible display device including a Laser Lift Off step (also referred to as an LLO step) described below is receiving attention.
FIGS. 8A to 8C are diagrams illustrating an LLO step included in steps of manufacturing a flexible organic EL display device.
As illustrated in FIG. 8A, a PI layer 102 made of, for example, a polyimide resin being a resin having a high heat resistance is first layered on a surface 101a on one side of a glass substrate 101 (non-flexible substrate) having a high heat resistance with a heat absorption layer (not illustrated) therebetween. A moisture-proof layer 103 being an inorganic film is layered on the PI layer 102. A TFT array layer 104 formed of a TFT element and an insulating film is formed on the moisture-proof layer 103. A first electrode (not illustrated) is patterned and formed on the TFT array layer 104 in association with an individual pixel by using a metal film in the same layer, and a terminal portion (not illustrated) is also formed on the TFT array layer 104. Then, any of a red light-emitting organic EL element 105R, a green light-emitting organic EL element 105G, and a blue light-emitting organic EL element 105B is formed on the first electrode. A sealing film 106 is formed to cover the red light-emitting organic EL element 105R, the green light-emitting organic EL element 105G, and the blue light-emitting organic EL element 105B.
Note that, each of the red light-emitting organic EL element 105R, the green light-emitting organic EL element 105G, and the blue light-emitting organic EL element 105B is, for example, a layered body of a hole injection layer, a hole transport layer, a light-emitting layer in each color, an electron transport layer, an electron injection layer, and a second electrode, all of which are not illustrated.
Subsequently, as illustrated in FIG. 8B, laser light irradiation is performed from the glass substrate 101 side. Accordingly, ablation occurs at an interface between the PI layer 102 and the glass substrate 101, and the glass substrate 101 is then peeled off from the PI layer 102.
Next, as illustrated in FIG. 8C, a back film 111 being a flexible substrate is bonded to the PI layer 102 with an adhesive layer (not illustrated) therebetween. The adhesive layer is provided on a surface 111a on one side of the back film 111. Then, the flexible organic EL display device is completed.
As described above, in a method for manufacturing a flexible organic EL display device that includes the above-described LLO step, a step of manufacturing a TFT element can be performed on the glass substrate 101 having a high heat resistance on which the PI layer 102 made of a polyimide resin being a resin having a high heat resistance and the moisture-proof layer 103 being an inorganic film are layered. Thus, the temperature of this step can be increased to about 450 degrees.
Therefore, when the LLO step is used, a TFT element and a display element having element performance and reliability being increased to a certain degree can be obtained.